Neuromuscular electrical stimulation (NMES) (also referred to as powered muscle stimulation, functional muscle stimulation, electrical muscle stimulation, and other terms) is an established technology with many therapeutic uses, including pain relief, prevention or retardation of disuse atrophy, and improvement of local blood circulation. NMES is typically delivered as an intermittent and repeating series of short electrical pulses. In many implementations, these pulses are delivered transcutaneously by surface electrodes that are attached to a person's skin. Electrodes may be held to the skin through the use of straps, adhesives, or other mechanisms, and often contain a coupling layer composed of gel or other materials that is capable of enhancing the efficiency of energy transfer from the electrode to the skin and underlying tissues.
A group of persons who could potentially show large benefit from NMES therapy are those who are immobilized or confined to bed rest. Periods of immobilization lead to muscle atrophy and weakness, and have severe effects on a person's physical capacity. Following immobilization, a previously active and functional person will typically require extensive physical therapy to reclaim their prior level of functionality. NMES may help these persons by preventing or retarding muscle atrophy during immobilization.
Critically ill medical patients comprise a subgroup of the immobilized persons described above. While virtually all of these patients are confined to bed rest, many are also suffering from conditions such as coma or are receiving interventions (such as mechanical ventilation) that generally require sedation and/or analgesia. These sedated or comatose patients are at the highest risk for muscle atrophy because even simple voluntary movements (such as shifting arms/legs in bed or moving one's feet) are often not performed. Consequently, critically ill patients face long paths to recovery that are generally measured in months as opposed to days or weeks.
As part of care for their acute illness, many critically ill patients receive I/V fluids, antibiotics, and other interventions. One common side effect of these medical treatments in immobilized patients is the development of tissue edema. Generally speaking, tissue edema occurs as body fluids accumulate in ‘the third space’, or the region outside of both cells and vessels. Edema is often caused by microvasculature leakage, and typically results in tissue swelling. This swelling has been known affect the ability of NMES to induce muscle contractions using surface electrodes placed on the skin. Increased electrical impedance and increased distance between surface electrodes and underlying muscles are factors that contribute to this problem. Although previous work in the medical literature has noted that certain types of electrical stimulation may prevent the onset of local edema after traumatic injury, these types of therapies have not been conclusively shown to prevent or reduce widespread edema.
Existing NMES devices do not have features or compensation mechanisms to address tissue edema. Because of this, these devices provide highly variable performance in and are of limited utility amongst patients suffering from this condition. For example, with existing NMES devices many patients in this group will require the delivery of much higher than average energy levels in order to transcutaneously stimulate muscle tissues. Performance variability increases labor costs associated with the delivery of NMES, and the requirement of using enlarged energy levels increases the potential for burns, muscle damage, and other adverse events. These factors and others limit the application of NMES therapy to edematous patients and to immobilized critically ill patients as a whole, a group that could benefit significantly from the therapy.
Therefore, a need exists for the delivery of safe and effective NMES therapy to immobilized critically ill patients, which could be facilitated by a device, system, and method designed to minimize the effects of tissue edema on NMES. Such a device, system, and method could allow for a larger patient cohort to receive the beneficial effects of a well established medical therapy.